A general bipolar stepping motor used in the analog electronic timepiece is a successful element in terms of low power consumption and reliable operation. It is configured to drive a wheel train connected to a second hand, a minute hand, and an hour hand by the 180-degree rotation of the rotor once in every second.
Such an analog electronic timepiece moves a second hand once in a second. Some users, however, prefer a continuous motion (also called sweep motion; can be an intermittent motion several to 10 several times in second) of a second hand of a mechanical timepiece. In the continuous motion, the second hand appears to fluently move. A demand therefor has been increasing in recent years.
To satisfy such a demand by use of a general stepping motor, the interval of drive timing needs to be shorted to increase a reduction ratio toward the second hand. However, the inertia ratio of the rotor is ineligible and accelerated at every driving of the wheel train. Excessive kinetic energy of the rotor is discarded in the process of the free damped oscillation. Because of this, along with an increase in the driving frequency, a rate of wasted power consumption increases, accelerating the weakening of batteries.
Among the analog electronic timepieces with the continuous second-hand motion, a wrist watch especially faces a large problem in terms of downsizing and thinning since it requires a large size of battery for a sufficient longevity.
Further, it is possible for the wrist watch to incorporate a generator such as solar battery in order to eliminate the need for battery replacement. However, such a non-battery replacing wrist watch cannot be realized since a large amount of power is consumed in continuous second-hand motion with use of a general stepping motor, which cannot be sufficiently supplied by a generator mounted in the wrist watch.
The inventors of the present invention took notice of too sufficient amount of output energy and torque from the axis of the second hand when the reduction ratio is set to a large value for the continuous motion. On the assumption that the power problem at a high-frequency motion could be overcome by reducing input energy, that is, input stroke, they decided not to rotate the rotor in the same direction but to reciprocate the rotor at a certain angle or oscillate it.
They studied related art to reciprocate a motion converter or change the direction of motion to thereby drive the wheel train of a timepiece, as disclosed in Patent Documents 1 and 2 below.
FIG. 16 is a plan view of the structure of an electric timepiece and the essential drive elements disclosed in Patent Document 1.
In FIG. 16 a rotor 163 reciprocates in horizontal direction. It is integrated with a feed tooth 1614a of a drive cam and includes driven wheels 1611, 1612 engaged with each other to drive the driven wheel 1611 counterclockwise by a half tooth by the clockwise rotation of the feed tooth 1614a from the position in the drawing. The other driven wheel 1612 is also rotated by the same amount. Then, the driven wheel 1612 is rotated clockwise by a half tooth by the counterclockwise rotation of the feed tooth 1614a. By reciprocating this motion, a fifth wheel 1613 is rotated in a certain direction by a constant amount.
Further, the document also discloses a reverse stop element 167 to position the teeth of the driven wheels and rotation stop teeth 1614b, 1614c to hit the teeth of the driven wheels to prevent excessive amplitude.
FIG. 17 is a plan view of the structure of a magnetic reverse escapement of an electric timepiece and the essential drive elements thereof disclosed in Patent Document 2.
In FIG. 17 the teeth of the two star wheels 171 has the same polarity at a tip side and opposite polarities on the side of a rotational shaft 172, and two gears 173 are coaxially adhered on the star wheels and engaged with each other. Because of this, the two star wheels 171 become stable in the state in the drawing or in a horizontally inverted state by magnetic attraction and repulsion. Hereinafter, the gears contacting or engaged with a drive source at a selected time are differentiated from the star wheels.
A magnet piece 174 is attached to an oscillation element 176 made of an oscillating permanent magnet, and reciprocates. The end of the magnet piece has the same polarity to that of the tooth tips of the two star wheels so that the star wheels are driven alternatively by magnetic repulsion with the teeth of the star wheels 171.
The related art in Patent Document 2 uses the two star wheels 171 driving together with the two gears 173. Because of this, the two driven wheels do not need to be engaged with a feed tooth unlike in Patent Document 1 shown in FIG. 16, and it is advantageous that the tooth shape of the star wheels 171 can be optimally designed for intrinsic feed operation.
Meanwhile, there is a known technique for oscillating the rotor to separately drive two gears in different directions (disclosed in Patent Document 3, for instance).
FIG. 18 is a plan view of the structure of a drive system of a crystal timepiece and the essential drive elements thereof disclosed in Patent Document 3.
In FIG. 18 a drive claw 1825a is fixed to the rotational shaft of an electromechanical converter which can rotate forward and reversely. The teeth of the second transmitting wheel 1833 are driven by a forward rotation signal which is generated in every second, to feed the second hand by a second-hand wheel 1827 connected with the second transmitting wheel 1833 and integrally moving with the second hand.
Further, it is reversely rotated by a reverse rotation signal which is generated at once in 10 seconds in a gap between second feed pulses, to drive the teeth of a fourth wheel 1834 connected with a minute hand and a hour hand.
That is, the drive claw 1825a has two edges facing the second transmitting wheels 1833 and fourth wheel 1834, in other words, includes two drive claws.
The teeth of the second transmitting wheel 1833 and fourth wheel 1834 are driven by a single tooth only when the drive claw 1825a moves in the normal directions. They are positioned by a positioning magnet 1840 so as to only shake and not to feed if touched while the claw moves in the opposite direction.
Thus, the related art disclosed in Patent Document 3 concerns a gear feeding mechanism by use of oscillation, however, the structure does not comprise the star wheels driving with the driven wheels as that disclosed in Patent Document 2.